This invention relates to a manual range-type transmission that incorporates a top cover assembly having a single shift rail, reverse bias, and shift housing.
Much effort is expended on designing transmissions that increases robustness and reliability while making the transmission easier to assemble and service. Manual transmissions incorporate many separate, non-integrated systems to achieve these ends.
In a manual range-type transmission for heavy duty trucks there is a set of gears in a main transmission section and a set of range gears that are actuated selectively to put the main transmission gears in either low or high range. After shifting through the main gears in low range, the operator may range shift to make available the main gears in high range, or vice versa. In this manner, the number of gears available to the vehicle operator is effectively doubled.
For the range gears to operate properly it is desirable that the transmission be in neutral (none of the main gears engaged) when a range shift occurs. Some prior art systems incorporate a three shift rail assembly that includes a check shaft that locks out the range gears when the main gears are not in neutral. However, these systems increase the shift effort necessary by the operator and still permits undesired range shifting in some instances.
Many manual transmissions for heavy duty truck applications do not have shift levers that automatically return to the neutral position when moved out of gear. The problem is that after the vehicle operator has moved the shift lever out of gear there is no feed back in the shift lever to indicated to the operator where he is in the shift pattern.
Further, manual transmissions may incorporate reverse biasing to indicate to the vehicle operator that the reverse gear is about to be engaged. This information is conveyed to the operator by a reverse biasing mechanism that increases resistance as the shift lever is moved in a horizontal direction towards a reverse gear position. Thus, while gear shifting the operator is alerted as to when the reverse gear is being approached. The operator can avoid inadvertently shifting into the reverse gear. Prior art systems incorporate additional components to achieve reverse biasing.
Moreover, manual transmissions include shift forks that are operatively connected to the shift lever. As the shift lever is moved throughout the shift pattern, a shift fork is selectively engaged and moves a clutch collar into engagement with a gear thereby causing a gear shift. The shift forks are often supported by the shift rail and typically include many fasteners and other components to attach the shift forks to the shift lever. These additional fasteners and components can make the transmission more difficult to shift and to manufacture and repair.
Therefore, what is needed is an assembly that integrates these functions into one conveniently manufactured and repairable assembly while still maintaining a reliable and durable transmission having an acceptable shift feel.